Cd Excluder Research Articles

Evaluation of heavy metal speciation distribution in soil and the accumulation characteristics in wild plants: A study on naturally aged abandoned farmland adjacent to tailings

Heavy metal composite pollution is widespread in the surrounding environment of tailings ponds in arid and semi-arid regions, leading to the abandonment of substantial agricultural land. This study investigates the speciation distribution and plant accumulation characteristics of heavy metals in abandoned farmland with different durations of natural aging. The aim is to comprehend the local heavy metal behavior pattern in the soil-plant system and offer insights for environmental remediation. Our findings reveal that Cd stands out as the primary heavy metal pollutant in this area. The mobility ranking of heavy metals is Cd > Pb > Zn > Cu, with Cd and Pb mobility decreasing along the basin. Notably, active Pb exhibits a higher affinity for soil binding compared to other metals. The predominant plant species in the region are primarily small shrubs, herbaceous plants, and semi-shrubs that demonstrate tolerance to drought and salt. Most plant samples showed elevated levels of Cd, Pb, and Zn, surpassing the maximum tolerance levels for dietary minerals in livestock. This elevated metal content poses potential threats to the health of local livestock and wildlife, yet it is also considered a potential for phytoremediation. Selected dominant plant species from the current study include Kalidium foliatum & gracile which shows potential as a Cd accumulator and indicator. Neotrinia splendens and Reaumuria songarica demonstrate potential as Cd excluders, with the latter exhibiting higher tolerance to Cd (62.9 mg/kg). Additionally, our observations indicate that different plant parts exhibit distinct responses to heavy metals, and Zn synergistically influences the aerial part accumulation of Cd.This study holds significant importance in understanding the complex behavior patterns of multi-metal pollutants in the natural environment. The identification of native plants with remediation potential is valuable for phytoremediation of environment pollution in mining area.

Bioavailability of Cd in Plantago weldenii and Sonchus oleraceus Plants: The Effects of a Humic and Fulvic Acids-Based Biostimulant

Cadmium (Cd) contamination poses a major threat to plants and human health, as well as to ecosystem services. Biostimulants provide a promising eco-friendly solution to enhance the phytoremediation of Cd-contaminated soils. We examined the influence of a humic and fulvic acids-based biostimulant on two plant species, e.g., Plantago weldenii and Sonchus oleraceus (common sowthistle), in a soil spiked with Cd at 45 mg kg−1. The aim of this study was to determine whether a biostimulant can potentially affect Cd mobility in soil and absorption in plant tissues. We found that the biostimulant significantly decreased Cd bioavailability (recorded as DTPA extractability) in the soil where Plantago was grown from 17.57 to 13.12 mg kg−1, probably due to the Cd immobilization effect of the added biostimulant. However, the biostimulant had the opposite effect in the soil where S. oleraceus was grown (Cd-DTPA significantly increased from 10.13 to 13.03 mg kg−1). S. oleraceus was found to have accumulated higher Cd concentrations in its aerial parts, resulting in a soil-to-plant transfer value close to 1 and root-to-shoot translocation value well above 1. These two indices exhibited the potential of S. oleraceus to be used as hyperaccumulator in Cd-contaminated soils, while P. weldenii behaved rather as a Cd excluder. These findings highlight the complex dynamics of added biostimulants and Cd behavior in soil and plants. We recognize the need for further research so that the mechanisms dictating Cd behavior after biostimulant application can be better elucidated.

Cd accumulation characteristics of Salvia tiliifolia and changes of rhizospheric soil enzyme activities and bacterial communities under a Cd concentration gradient

This study aimed to explore the phytoremediation potential of Salvia tiliifolia for cadmium (Cd)-contaminated soils and to understand the interactions in soil-Cd-plant systems. We assessed the Cd tolerance and accumulation characteristics of S. tiliifolia grown in soils with 0, 5, 25, and 50 mg kg− 1 Cd for 3 months. We also analysed the changes in physicochemical properties, enzyme activities, and bacterial community composition in the rhizosphere soils of S. tiliifolia. S. tiliifolia could tolerate all Cd concentrations with unchanged biomass. Cd concentrations (21.50–189.50 mg kg− 1) in roots of S. tiliifolia and corresponding bioconcentration factors (3.79–4.30) were much higher than those in shoots, and Cd translocation factors (0.03–0.23) were thereby very low. Rhizosphere pH decreased with increasing concentrations of Cd. Soil pH and rich organic matter may jointly affect the soil available Cd. Ultimately, soil enzyme activities involved in carbon, nitrogen, and phosphorus cycles were affected to varying degrees, and bacterial diversity and richness were slightly influenced by Cd stress. Interestingly, bacterial ABC transporters were induced by Cd stress during this process. S. tiliifolia can be designed as a Cd excluder. The induced soil bacterial ABC transporters may contribute to Cd detoxification and accumulation in both soil microbial communities and S. tiliifolia plants.

Morphological Responses and Gene Expression of Grain Amaranth (Amaranthus spp.) Growing under Cd.

Phytoremediation efficiency depends on the ability of plants to accumulate, translocate and resist high levels of metals without symptoms of toxicity. This study was conducted to evaluate the potential of grain amaranth for remediation of soils contaminated with Cd. Three grain amaranth varieties, “Pribina” (A. cruentus), “Zobor” (A. hypochondriacus x A. hybridus) and Plainsman (A. hypochondriacus x A. hybridus) were tested under different level of Cd (0, 5, 10 and 15 mg/L) in a hydroponic experimental treatment. All could be classified as Cd excluders or Cd-hypertolerant varieties able to grow and accumulate significant amounts of Cd from the hydroponic solution, preferentially in the roots. Under the highest level of Cd exposure, qRT-PCR expression analysis of five stress-related genes was examined in above- and below-ground biomass. The results show that the Cd concentration significantly increased the mRNA level of chitinase 5 (Chit 5) in amaranth roots as the primary site of metal stress. The involvement of phytochelatin synthase (PCS1) in Cd detoxification is suggested. Based on our findings, we can conclude that variety “Pribina” is the most Cd-tolerant among three tested and can be expected to be used in the phytomanagement of Cd loaded soils as an effective phytostabiliser.

Patterns of cadmium uptake and accumulation by exclusion and inclusion soybean cultivars

AbstractIn the areas where the soils are polluted by cadmium (Cd), farmers cannot afford to use their lands for remediation due to high demand for soybean (Glycine max L.) production. In order to provide information for safe soybean production and achieve the phytoremediation using the root at the meantime, four soybean cultivars (mentioned as Cd excluder and Cd includer) differing in seed Cd accumulation were grown in a mixed growing media treated with different Cd concentrations (0 and 0.35 mg kg−1) in a growth cabinet. The biomass and Cd concentration in roots, stems, leaves, pods, and seeds were measured at the beginning of seed development (R5) and maturity (R8) stages; accumulation coefficient and translocation coefficient of Cd in different organs were calculated. Cadmium concentration in seeds was positively correlated with the Cd concentration in stem, leaf, and pod. Cadmium concentration in the roots of the Cd excluder was significantly higher than that in the Cd includer at the R5 and R8 stages; however, the Cd concentration in the seeds of the Cd includer was higher than that in the Cd excluder. Compared with the Cd excluder, more Cd was transported from the root to the aboveground organs of Cd includer. This suggests that Cd excluder with high cadmium accumulation in the root and low accumulation in the seed could provide a possible way to develop Cd‐safe cultivars with high phytoremediation capacity when grown on Cd‐polluted lands.

Naturally selected dominant weeds as heavy metal accumulators and excluders assisted by rhizosphere bacteria in a mining area.

Managers need more practical and promising plants for use in heavy metal phytoremediation. Although previous studies have identified the potential of some weeds and microbial strains in phytoremediation, the potential of dominant weeds and the relationship between weeds and their rhizosphere bacterial strains are still unknown. In our study, we examined dominant weeds in the Dabaoshan mine located in Guangdong province, China to test their abilities as heavy metal accumulators and excluders. Results suggest that Ludwigia prostrata exhibited the highest potential for accumulating Cu, Pb and Zn compared with the other plants. Specifically, L.prostrata accumulated 71.58, 130.76 and 454.72 mg kg-1 of Cu, Pb and Zn, respectively; the species' translocation factor of Zn was 2.04, indicating a high accumulation of Zn. In contrast, the Cd translocation factor (TF) of Digitaria sanguinalis was 0.18, significantly lower than that of other plant species examined. Our results suggest that Ludwigia prostrata hyperaccumulates Zn and may also serve as a potential candidate remediation plant for Cu and Pb due to its high absolute accumulation amount of Cu and Pb, while Digitaria sanguinalis may be a potential candidate as a Cd excluder. We also found that rhizosphere bacterial communities were shaped by individual dominant plant species. Chloroflexi was the most dominant phylum in accumulator plant such as Fimbristylis miliacea, while Cyanobacteria was the most dominant phylum in excluder plant such as Digitaria sanguinalis. Our study provides insights for selecting new weedy forbs and grasses, rhizosphere bacterial species and developing approaches for phytoremediation and phytostabilization.

Ability of Cytisus scoparius for phytoremediation of soils from a Pb/Zn mine: Assessment of metal bioavailability and bioaccumulation

Abandoned mining areas are an environmental concern for aquatic and terrestrial ecosystems due to their unfavourable soil properties and high levels of potentially toxic elements. Despite this, some plant species may grow spontaneously and colonise these areas; being suitable in many cases for restoration practices, since they may accumulate metals in their tissues. This study aims to assess the effectiveness of 14 chemical soil extractants to predict the bioavailability of toxic elements (Cd, Pb and Zn) in soils from the abandoned Pb/Zn mine of Rubiais (NW Spain), based on root and shoot metal contents in Cytisus scoparius (L.) Link, which grows spontaneously in this area. Afterwards, its potential for phytoremediation activities was assessed. Mine soils showed high contents Cd (1.77–14.38 mg kg−1), Pb (850–2137 mg kg−1) and Zn (1754–12090 mg kg−1). Cytisus scoparius grows in spite of these high metal contents; accumulating Zn and Pb in its roots, Zn in the aerial part and excluding mostly Cd from its tissues. None of the extractants used to determine the bioavailable content of Pb allow predicting its availability for C. scoparius. However, LMWOA was the most effective extractant to determine the bioavailability of Cd and Zn for this species. Besides, NH4NO3 and Ca(NO3)2 are also good indicators for Zn bioavailability. The analysis of bioconcentration and translocation factors suggest that C. scoparius behaves like a Zn accumulator plant, whereas alternatively, it behaves like a Pb phytostabiliser and as a Cd excluder species. Thus, C. scoparius can be used as a species for mine soil restoration, decreasing the mobility of metals and preventing their dispersion to another ecosystem compartments.

Effect of Cd on growth, physiological response, Cd subcellular distribution and chemical forms of Koelreuteria paniculata

Koelreuteria paniculata were cultivated in nutrient solution with different concentrations of Cd (0, 50, 150, 250 and 500 µM) and sampled after 90 days. The resistance, translocation, accumulation and stress responses in Koelreuteria paniculata were investigated by hydroponic experiments. The results showed that Koelreuteria paniculata is an efficient Cd excluder that can tolerate high concentrations of Cd (up to 150–250 µM of Cd). The concentration of Cd never exceeds 5 ppm in leaves and 10 ppm in roots. The high concentration of Cd (≥ 250 µM) had a toxic effect on K. paniculata and significantly restricted the plant growth. The accumulation ability of Cd by different plant tissues followed the sequence of roots > leaves > stems. The bioconcentration factors and translocation factors both were less than 1. Cd has the highest content in the cell wall and is migrated to soluble fractions and organelles at high concentrations. Undissolved Cd phosphate, pectates and protein-bound Cd were the predominant forms. The low concentration of Cd (≤150 µM) promoted the synthesis of soluble proteins, AsA and GSH, while high concentration of Cd clearly inhibited the physiological and biochemical process, caused membrane lipid peroxidation and severe membrane damages, and increased MDA and H2O2 contents. POD, CAT and SOD exhibited positive and effective responses to low concentration Cd stress, but could not remove the toxicity caused by high concentration Cd stress. The content of IAA, GA and ZT decreased and ABA content was significantly increased under high-concentration Cd stress.

Influence of amendments on Cd and Zn uptake and accumulation in rice (Oryza sativa L.) in contaminated soil.

Cadmium is a toxic metallic element that poses serious human health risks via consumption of contaminated agricultural products. The effect of mixtures of dicalcium phosphate and organic amendments, namely cow manure (MD) and leonardite (LD), on Cd and Zn uptake of three rice cultivars (KDML105, KD53, and PSL2) was examined in mesocosm experiments. Plant growth, Cd and Zn accumulation, and physicochemical properties of the test soils were investigated before and after plant harvest. Amendment application was found to improve soil physicochemical properties; in particular, soil organic matter content and nutrient (N, P, K, Ca, and Mg) concentrations increased significantly. The MD treatment was optimal in terms of increasing plant growth; the MD and LD treatments decreased soil Cd concentration by 3.3-fold and 1.6-fold, respectively. For all treatments, all rice cultivars accumulated greater quantities of Cd and Zn in roots compared with panicles and shoots. Among the three cultivars, RD53 accumulated the lowest quantity of Cd. Translocation factors (<0.28) and bioconcentration coefficients of roots (>1) indicate that the three rice cultivars are Cd excluders. Our results suggest that a mixture of organic and inorganic amendments can be used to enhance rice growth while reducing accumulation of heavy metals when grown in contaminated soil.

Accumulation of Cd, Cu and Zn in shoots of maize (Zea mays L.) exposed to 0.8 or 20 nM Cd during vegetative growth and the relation with xylem sap composition.

This work focuses on the exposure of maize plants to nanomolar concentrations of Cd, which is relevant for agricultural soils cropped with food and feed plants. Maize plants were cultivated in nutrient solution at 0.8 or 20 nM Cd during the vegetative growth stages. No significant hormesis or toxic effects of Cd were observed on maize growth, but a decrease in the allocation of Cd to shoots between the 0.8 and 20 nM Cd exposures revealed that the plants already responded to these low concentrations of Cd according to a shoot Cd excluder strategy. The Cd, Cu and Zn concentrations in shoots decreased with time as the result of an early decrease in the root/shoot ratio and of a decrease in the coefficient of allocation to aboveground for Zn and Cd at 20 nM. As a consequence, shoots of young plants were richer in micronutrients Cu and Zn but also in toxic Cd. The rate of delivery of Cd, Cu and Zn from xylem sap was successfully used to predict the time course of concentrations of Cd, Cu and Zn in the shoot. However, it overestimated the actual concentrations of Cd in the shoot, presumably because the reallocation of this trace element from shoots back to roots was not taken into account.

Effect of cadmium on growth, photosynthesis, mineral nutrition and metal accumulation of bana grass and vetiver grass

An experiment was conducted to evaluate the differential effects of Cd contamination on the growth, photosynthesis, mineral nutrition and Cd accumulation of bana grass (Pennisetum americanum×Pennisetum purpureum) and vetiver grass (Vetiveria zizanioides). Bana grass accumulated 48–453 and 25–208mgkg−1 in plant roots and shoots, respectively, at 15–100mgkg−1 soil Cd concentration, while vetiver grass accumulated 167–396 and 0.13–9.0mgkg−1. These results indicated that bana grass was a Cd accumulator while vetiver grass was a Cd excluder. The ratio of root to shoot biomass was significantly increased in vetiver grass, while it was unchanged in bana grass by Cd pollution. This suggests that excluders may allocate more energy to roots than shoots under Cd pollution compared to un-contaminated condition, while accumulators may allocate equal proportions of energy to roots and shoots. For bana grass, soil Cd pollution significantly decreased the concentration of Fe and Mn in roots as well as the translocation factors of Zn and K. For vetiver grass, soil Cd pollution significantly decreased the concentration of Fe in roots and had no influence on the translocation factors of Fe, Mn, Cu, Zn, Mg, K and Ca. Soil Cd pollution showed no significant effect on chlorophyll content and photosynthetic rates in either of the grasses. The water content and leaf transpiration rate were significantly increased by Cd pollution in bana grass, while they were unchanged in vetiver grass. The results indicated that the energy allocation and mineral nutrition characteristics may aid in screening suitable plant species for phytoremediation.

Cadmium minimization in rice. A review

Cadmium (Cd) contamination of rice is found in areas irrigated by wastewater from mines. Cd contamination of rice fields can also result from the application of Cd-rich phosphate fertilizers. As a consequence, millions of tons of rice are discarded. In Asia, irrigated paddy-based cropping systems provide rice grains as food for about 2 billion people. A daily intake of 20–40 μg Cd from rice is reported in regions where rice is used as a food. Daily rice Cd intake leads to diseases such as bone mineralization. Hence, Cd minimization in rice is needed. This article reviews sustainable agriculture and molecular techniques that prevents Cd uptake in rice. Cadmium minimization can be done either by field remediation or change in plant functions. Organic farming decreases Cd uptake and remediates crop fields. Cd hyperaccumulator plants and Cd immobilizing microbes can be used for field remediation. Cd amount in rice can be controlled by gene families that code for putative transition metal transporters or metal chaperones and quantitative trait loci (QTL). Generation of Cd excluder rice is possible by transgenics.

An assessment of Agropyron cristatum tolerance to cadmium contaminated soil

A pot experiment was conducted in a greenhouse to assess the tolerance of Agropyron cristatum plants to cadmium contaminated soils (0, 5, 10, 25, 50, 100, 150, and 200 mg kg−1) for 100 d. Results indicate that Cd in concentrations of 5–50 mg kg−1 had no significant impact on growth, relative membrane permeability (RMP), lipid peroxidation measured as malondialdehyde (MDA) content, and chlorophyll (Chl) content relative to the control. Exposure of these plants to high concentrations of Cd (100–200 mg kg−1) caused a small reduction in growth and Chl content and a slight enhancement of RMP and MDA content compared with the control. In addition, superoxide dismutase (SOD) and peroxidase (POD) activities show an increasing trend with the increase of Cd content in soil. The Cd content in the roots was 4.7–6.1 times higher than that in the shoots under all Cd treatments suggesting that the plant can be classified as a Cd excluder. The translocation factor was low and similar at 25–200 mg kg−1 Cd treatments. In summary, A. cristatum plants tolerated Cd stress and might have potential for the phytoremediation of Cd contaminated soils.

Salicylic acid-mediated alleviation of cadmium toxicity in hemp plants in relation to cadmium uptake, photosynthesis, and antioxidant enzymes

To assess the role of salicylic acid (SA) in alleviating cadmium (Cd) toxicity in hemp (Cannabis sativa L.) plants, the growth parameters, Cd accumulation, photosynthetic performance and activities of major antioxidant enzymes were investigated in hemp seedlings treated with 500 μM SA, under 0, 25, 50, and 100 mg Cd kg−1 sands (DW) conditions, respectively. Cd exposure resulted in a small reduction in biomass (12.0–26.9% for root, and 8.7–29.4% for shoot, respectively), indicating hemp plants have innate capacity to tolerant Cd stress. This was illustrated by little inhibition in photosynthetic performance, unchanged malondialdehyde content, and enhancement of superoxide dismutase (SOD) and peroxidases (POD) activities in hemp plants. Cd content in root is 25.0–29.5 times’ higher than that in shoot, suggesting the plant can be classified as a Cd excluder. It is concluded that SA pretreatment counteracted the Cd-induced inhibition in plant growth. The beneficial effects of SA in alleviating Cd toxicity can be attributed to the SA-induced reduction of Cd uptake, improvement of photosynthetic capacity, and enhancement of SOD and POD activities.

Phytochelatin Concentrations and Binding State of Cd in Roots of Maize Genotypes Differing in Shoot/Root Cd Partitioning

To investigate Cd binding in the root system as a possible cause of differential Cd distribution in maize inbred lines, Cd present in ‹soluble› and ‹insoluble pools› in roots of a ‹shoot Cd excluder› (B73) and a ‹non-shoot Cd excluder› (H98) was determined after extraction of the roots in HEPES buffer solution (pH 6.5). At a similar root Cd concentration (approximately 70 μg Cdg-1dry wt.), about 49 % of the Cd concentration in roots of H98 but 25 % of that in roots of B73 was removed during extraction (‹soluble pooh›). The acid-soluble thiol concentrations in roots of the ‹shoot Cd excluder› B73 were much lower compared with those of the ‹non-shoot Cd excluder› H98. Exposure of B73 and H98 plants to the same Cd concentration in solution resulted in nearly equal acid-soluble thiol concentrations in the root extracts. Binding characteristics of Cd to structural components of the roots (‹insoluble pool›) were similar for both maize inbreds. The relationship between transport of Cd from roots to shoots and amounts of Cd complexed to acid-soluble thiol compounds in the ‹soluble pool› of ‹non-shoot Cd excluders› compared with ‹shoot Cd excluders› is discussed.

Evaluation of structural and physiological plant characteristics in relation to the distribution of cadmium in maize inbred lines

To establish the structural and physiological characteristics related to the genotypic variation in Cd distribution between maize inbred lines (‘shoot Cd excluders’ and ‘non-shoot Cd excluders’), shoot and root morphological parameters were studied on plants grown in nutrient solution. Furthermore, the xylem sap composition and the desorbability of Cd from roots of these inbreds have been compared. No relationship between the morphological characteristics of either shoot (specific leaf area and leaf area ratio) or root (specific root length, specific surface area, and average diameter) and Cd distribution could be assessed. Cadmium concentrations in the xylem exudates from ‘non-shoot Cd excluders’ were higher than those from ‘shoot Cd excluders’, but not related to citrate and malate concentrations. The absolute and relative amounts of Cd desorbed from roots of ‘shoot Cd excluders’ were about twice as high compared to those of the ‘non-shoot Cd excluders’, especially at the lowest Cd concentration in solution. The absence of a relationship between shoot or root morphological parameters and Cd partitioning and the differences between both groups in the amounts of Cd desorbed, even at similar root Cd concentrations, indicate that the differential Cd distribution between ‘shoot Cd excluders’ and ‘non-shoot Cd excluders’ may be related to the observed differences in root Cd concentration, desorption characteristics and binding capacity of Cd inside and/or outside the root and its distribution within the roots.

Cadmium distribution in maize inbred lines: Effects of pH and level of Cd supply

In order to investigate the physiological basis of the differential Cd distribution and the degree of variation of this Cd distribution among maize inbred lines, six inbreds designated earlier as ‘shoot Cd excluders’ (B73, H99, and H96) and ‘non-shoot Cd excluders’ (B37, H98, and N28) were grown in nutrient solution culture at different external Cd levels or at different pH. The characterization of the inbreds according to their shoot/root partitioning of Cd was consistent, independent of pH or level of Cd supply. The Cd concentrations in the plants were highest at the highest pH of the solution cultures. Generally, there was a positive correlation between the Cd concentrations in shoots and xylem exudates. It was shown that the Cd concentration in the roots is particularly important in the Cd distribution process. Above a ‘critical’ internal Cd concentration in the roots, specific for each inbred, the ability to retain Cd is strongly diminished. It is concluded that structural and/or physiological characteristics of the roots are involved in Cd partitioning.

Uptake and distribution of cadmium in maize inbred lines

Genotypic variation in uptake and distribution of cadmium (Cd) was studied in 19 inbred lines of maize (Zea mays L.). The inbred lines were grown for 27 days on an in situ Cd-contaminated sandy soil or for 20 days on nutrient solution culture with 10 µg Cd L-1. The Cd concentrations in the shoots showed large genotypic variation, ranging from 0.9 to 9.9 µg g-1 dry wt. for the Cd-contaminated soil and from 2.5 to 56.9 µg g-1 dry wt. for the nutrient solution culture. The inbred lines showed a similar ranking for the Cd concentrations in the shoots for both growth media (r2=0.89). Two main groups of inbreds were distinguished: a group with low shoot, but high root Cd concentrations (shoot: 7.4±5.3 µg g-1 dry wt.; root: 206.0±71.2 µg g-1 dry wt.; ‘shoot Cd excluder’) and a group with similar shoot and root Cd concentrations (shoot: 54.2±3.4 µg g-1 dry wt.; root: 75.6±11.2 µg g-1 dry wt.; ‘non-shoot Cd excluder’). The classification of the maize inbred lines and the near equal whole-plant Cd uptake between the two groups demonstrates that internal distribution rather than uptake is causing the genotypic differences in shoot Cd concentration of maize inbred lines. Zinc (Zn), a micronutrient chemically related to Cd, showed an almost similar distribution pattern for all maize inbred lines. The discrepancy in the internal distribution between Cd and Zn emphasizes the specificity of the Cd distribution in maize inbred lines.